John, a Tuscan, the Archdeacon of the Roman clergy, was elected to succeed St. Hormisdas, but he was not to enjoy the same prosperity as his predecessor. Now that the Acacian schism had ended in the East and an orthodox emperor ruled at Constantinople, the hitherto mild Theodoric began to make trouble at home. The Ostrogoth king was growing old and suspicious. He regarded the new friendliness between Rome and Constantinople as a possible danger to his regime. His suspicion rose to fury when he heard that Emperor Justin had taken measures against the Arian heretics in the East and had deprived them of their churches. The angry Goth seems at first to have thought of waging war in favor of his fellow Arians. Then he decided to see what he could accomplish by an embassy. He summoned Pope John to Ravenna and imposed upon him the decidedly disagreeable task of going to Constantinople at the head of this embassy to ask the orthodox emperor to restore the churches to the Arians. John objected, but Theodoric packed him and the embassy on board ship and away they sailed for Constantinople.

The mission was embarrassing but the journey glorious. Wherever they stopped the Pope was hailed with joy, and when they approached Constantinople, Pope John was met at the twelfth milestone by a brilliant procession of clergy carrying crosses and candles.

Emperor Justin received him with the highest honors. On Easter Sunday, April 19, 526, he celebrated Mass in Sancta Sophia. He crowned the Emperor. He received enthusiastic pledges of loyalty from the Eastern bishops. Alexandria alone, now hardening in its Monophysite heresy, remained aloof.

This glorification of Pope John by the devout people of Constantinople was his Thabor. Calvary was before him. Theodoric was waiting for him, now a brutal Theodoric who had just butchered the gentle philosopher Boethius and the senator Symmachus. When the Pope got back to Ravenna Theodoric threw him into prison. Already tired by his journey and worn by new sufferings, Pope John did not last long in a prison cell. He died May 18, 526. He was buried outside the walls of Ravenna, but later his body was brought back to Rome and buried in St. Peter's. St. John is honored by the Church as a martyr; his feast is kept on May 27.